Loimia medusa ( Savigny, 1818 )

Londoño-Mesa, Mario H. & Carrera-Parra, Luis F., 2005, Terebellidae (Polychaeta) from the Mexican Caribbean with description of four new species, Zootaxa 1057, pp. 1-44 : 17-19

Loimia medusa ( Savigny, 1818)

Figures 4 G–J

Material examined: Mexican Caribbean: ECOSUR TERE­8 (1) Punta Allen, 10 Jun. 1986, 2 m. (1) QR7 Chankanaab, Cozumel Island (20°56’38’’N 86°59’35’’W), 2 Apr.1992, 2 m. (1) Blanquizal, Bajo Pepito, Mujeres Island, Feb. 1997, 2 m, in Halimeda incrassata . (1) Blanquizal, Bajo Pepito, Mujeres Island, Mar. 1997, 2 m. (1) Xahuayxol (18°30’15’’N 87°45’32’’W), 2 Jun. 1997, 1.5 m. (1) Punta Nizuc, Cancún (21°02’11.7’’N 86°46’ 44.2’’W), 30 Aug. 1997, 2 m. (1) Punta Nizuc, Cancún (21°02’11.7’’N 86°46’44.2’’W), 1 Sep. 1997, 2 m. (1) Leeward of Contoy Island (21°30’8.4’’N 86°47’45.3’’W), Jun. 1999, 3.5 m. (1) Majahual (18°40’09.6’’N 87°43’01.4’’W), 19 Jan. 2001, 1.5 m. (1) Majahual (18°40’09.6’’N 87°43’01.4’’W), 24 Feb. 2001, 2 m, in coralline rock. (2) Lighthouse, Contoy Island (21°30’34’’N 86°47’47’’W), 1 Mar. 2001, 2 m. (1) R/V “Edwin Link”, sta. 2780 Northern Blackford Cay, Chinchorro Bank (18°30’94’’N 87°26’61’’W), 22 Aug. 1990. Gulf of Mexico: (5). Ría Lagartos (21°37’16.7’’N 88°10’32.6’’W), coralline rock, 18 Feb. 1999, 1– 2 m.

Description: Specimen complete, with 99 segments, 19 mm long; thorax 8 mm long, 2 mm ( Figure 4 G). Tentacles short; tentacular membrane not extending ventrally; uncovering the ventral side. Eyespots absent. Upper lip with a long free edge projecting forwards, spoon­like, longer than wide; thicker basally; lower lip swollen partially covered by a membrane that connects ventrally the first pairs of lateral lappets. With 2 pairs of lateral lappets, discontinuous, on segments 1 and 3, first covering the tentacular membrane and the lower lip, ventrally; second pair of lateral lappets reaching the base of first pair, laterally covering segment 2, with well developed dorsal lobe reaching the bases of first and second pairs of branchiae; ventrally, the base of the lappet and the first and second ventral shields clearly discontinuous; its ventral lobe does not extend towards ventral side. Three pairs of branchiae presented, branched, on segments 2 to 4; first and second pairs slightly longer than third pair; branchiae with long and thin stalks, and many short dendritic branches. Nephridial papillae absent. Eleven ventral shields, starting from segment 2 ( Figure 4 H); first, second and part of third shield fused and wrinkly, remaining shields almost all equal­sized. Abdomen with midventral groove. Notopodia from segment 4, extending through 17 segments; notochaetae long, smooth, narrowly bilimbate ( Figure 4 I); all similar in length within each fascicle, or gradually decreasing in size, but with the same shape. Neuropodia from segment 5; arranged in single row until segment 10, in double rows from segment 11–20, in back to back position; in single rows from segment 21 until the pygidium. Neuropodia wider on thorax, abdominal ones narrower and longer, tapering in size to the pygidium; uncini with the same shape throughout. Uncini pectinate with 5 teeth ( Figure 4 J); upper subrostrum rounded, subrostral process small, anterior process short, sometimes with attached filament; basis rounded terminating in a conspicuous posterior process, with filament attached; occipitium rounded and curved finishing in the upper tooth of capitium. Pygidium rounded, without anal papillae; anus terminal.

Var ia t io n: The number of ventral shields varies from 14 to 16. Some specimens with eyespots. The total number of segments in all specimens complete revised varies from 57 to 114 segments.

Remarks: It was not possible to find any morphological difference between the type (Neotype LACM­AHF Poly 1656, from Persian Gulf) and the specimens from Mexico. This is probably another complex of sibling species, and future studies on reproduction and molecular analyses could be helpful to separate populations into different species. Hutchings & Glasby (1995) mentioned that it is difficult to determine if the second pair of lateral lappets rises from the second or third segments. According to our viewpoint, this pair of lateral lappet is derived from the third segment, because segment two is greatly reduced. We can notice this because notopodia start on segment 4 in this genus, and by methyl green staining; the boundary between third and fourth segments is distinguished as a thin stained line. Thus, this species presents discontinuous lateral lappets on segments 1 and 3.

Distribution: Probably circumtropical

Figures

FIGURE 4. Eupolymnia crassicornis: A. Lateral view; B. Chaeta from segment 5; C. Uncinus from segment 5. Eupolymnia nebulosa: D. Lateral view; E. Chaeta from segment 10; F. Uncinus from segment 10. Loimia medusa: G. Lateral view; H. Ventral view; I. Chaeta from segment 8; J. Uncinus from segment 8. Scale bars: A 4 mm; B, E, I 0.05 mm; C, F, J 0.02 mm; D, G, H 2 mm.